Optical sensor systems may include source modules and detection modules to detect the presence of objects there between. The source modules and detection modules may include respective window members. The source module may emit a detection signal such as an infrared signal through the respective window members to be received by a detection module. The objects such as volatile organic compounds (VOC) may be detected when present in a path of the detection signal. Such optical sensor systems may be included in image forming apparatuses, air quality monitoring devices, or the like.